It has been a week, but I thought I'd bump this. I, too, am running CM11 nightlies, ART, but on oooold hardware SGS2 (T989 Hercules). Have tried everything (reasonable) to get it functioning again. Looked at the already noted bug report that has been fixed/closed. There is something weird: When I looked for files from the failed install, it shows a file fragment that says Dalvik. My hunch is that this version of Whatsapp is looking for Dalvik on some devices that are running ART, when it doesn't find it, it fails. I don't think this is an AOSP or CM issue. I think this is a Whatsapp bug.